The proposed research comprises an attempt to increase knowledge of language acquisition processes, by the intensive investigation of children's knowledge of the grammatical system of conjunction at designated points before and immediately after its use becomes stable in spontaneous speech. In particular, major posed problems are 1) whether children's pre-spontaneous competence in three major syntactic types of conjunction (sentential, predicate, and noun phrase conjunction) develops simultaneously, as it appears to do in spontaneous speech, or whether pre-spontaneous competence develops in one or another type sooner, and 2) once the system becomes productive in spontaneous speech, whether the apparent strong initial semantic constraints on conjunction are truly characteristic of the child's underlying system, or whether such constraints appear to be operating only because of sampling and/or performance problems. Answers to both these questions lead t different formulations of the child's natural rule-forming capacities and strategies. The major method of investigation consists of having the children imitate grammatical and ungrammatical instances of conjunction at three specified points of grammatical development before spontaneous use of conjunction and at one point immediately afterwards. In an effort to increase the quality and quantity of data, parents will be asked to participate extensively as experimenters for their own children, being models for sentences to be imitated. The study will consist of a mixed cross-sectional short-term longitudinal design; most children will be seen at least two of the four investigatory points, in order to investigate intra-individual consistency and inter-individual variation and consistency, but no child will be seen at all four designated investigation points.